What is the difference between normal theme and the child theme?

A parent theme is a stand alone theme which have no dependencies on other themes. A parent theme is fully functional on its own without the need for any other features from any other theme.

A child theme cannot function on its own without the parent theme. The child theme inherent the functionality of the parent theme. A child theme may only contain one style.css file and a few lines of CSS which change the appearance of the parent theme whereas a parent theme contains a complete file structure with templates and a fully coded style sheet.

We are recommending to use a child theme, you can easily modify your wordpress website using child themes without ever changing the parent theme. When a new version of the parent theme appears, you can safely update it as all your modifications are saved in the child theme.

If you are using parent theme and made some theme customization you need to transfer all customizer setting to child after you activate it, then you can make update without loosing your theme changes.